How long does it take to form a habit, according to research?
In the best-known study, Lally et al. (2010) found that a simple daily behavior took a median of about 66 days to feel close to automatic, with a range of 18 to 254 days among 96 volunteers. A 2024 systematic review by Singh et al. found median times of 59 to 66 days across studies, with individuals ranging from 4 to 335 days.
So the honest answer is: often around two months for a simple daily action, and much longer for some people and some habits. No single number applies to you.
What did the studies actually measure?
The numbers above measure automaticity, which is how much a behavior happens without deliberate thought. Participants rated this themselves every day or at set points.
In Lally's study, 96 volunteers each chose one eating, drinking or activity behavior, such as drinking water after breakfast, and did it daily in the same context for 12 weeks. Of the 82 who gave enough data, the researchers could model a clear curve for 62. The 66-day figure is the median time for those people to reach 95% of their own automaticity plateau, often estimated beyond the 12 weeks of the study.
The Singh review pooled 20 studies with 2,601 participants. Only four of them reported time to habit formation. Medians ranged from 59 to 66 days and means from 106 to 154 days. The authors note that most studies had a high risk of bias and the evidence base is small, with flossing and diet studied most.
| Study |
Who took part |
Time to habit |
| Lally et al. (2010) |
96 adults, one simple daily behavior each |
Median about 66 days; range 18 to 254 |
| Keller et al. (2021) |
192 adults, a daily nutrition behavior |
Median 59 days among those who formed a habit; range 4 to 335 |
| Singh et al. (2024) review |
20 studies, 2,601 participants |
Medians 59 to 66 days; means 106 to 154 days |
In Keller's trial, the review reports that only 23% of participants reached the study's threshold for habit formation. Many people in these studies did not get there within the study period at all.
What speeds habit formation up, and what slows it down?
Speed depends on the habit, the setup and the person. This table combines what the review found with the practical setup that follows from it.
| Factor |
Tends to speed it up |
Tends to slow it down |
| Consistency |
Doing it on most days |
Frequent skipped days |
| Context |
Same place and same cue each time |
A different time and place every day |
| Choice |
A habit you picked yourself |
A habit someone assigned to you |
| Plan |
A specific if-then plan ("After coffee, I…") |
A vague intention ("I will exercise more") |
| Enjoyment |
An action you find pleasant or satisfying |
An action you dread |
| Timing |
Morning practice, in one stretching study |
Evening practice, in the same study |
| Size |
A small, simple action |
A long, multi-step routine |
The timing row comes from a stretching study summarized in the Singh review: mean time to habit was 106 days for morning stretching and 154 days for evening stretching. That is one study of one behavior, so treat it as a hint, not a rule. The consistency row comes from Lally, where people who did the behavior more consistently fit the habit curve better.
Where did the 21-day idea come from?
The 21-day idea traces back to Psycho-Cybernetics, a 1960 self-help book by the plastic surgeon Maxwell Maltz. He observed that people seemed to need a minimum of about 21 days to adjust to changes, such as a new appearance after surgery.
That was an observation from his practice, not a study of habit formation. Over time, "a minimum of about 21 days" was retold as "21 days to form a habit." The Singh review states that its findings refute the popular 21-day notion.
What should you do during each stage?
These stages are rough guides, not deadlines. Your own timing may be faster or slower.
Weeks 1–2: make it easy to start
Pick one small habit and tie it to a stable cue. Write it as "After I [cue], I will [action]." Our habit stacking builder helps you find a reliable anchor. Keep a 2-minute version for busy days and mark each start on a habit tracker.
Weeks 3–6: protect the cue
The early novelty fades here, and effort can still feel high. Keep the same cue and place. If the same days keep slipping, change one thing, such as the time or where you keep what you need. Do not add a second new habit yet unless the first feels easy.
Weeks 7–10 and beyond: notice, then decide
Many people start to notice the habit happening with less thought around now, but many do not. If it still takes effort, that is normal and not a sign of failure. Keep going with the same setup. If it has become easy, you can extend the habit slightly or start a second one.
Does missing a day reset your progress?
No. In Lally's study, missing one opportunity to do the behavior did not materially affect the habit formation process. What mattered more was repeating the behavior in a consistent context over time.
The practical rule is to never miss twice in a row. After a missed day, go back to your usual cue the next day. Do not double up to make up for it. Our guide on how to use a habit tracker explains how to mark missed and hard days without losing the pattern.
When does the timeline look different?
If the habit is complex
A full workout, a cooking routine or a study session has many steps. Build the first step into a habit, such as putting on workout clothes, and let the rest follow. See the difference between a habit and a routine for why this matters.
If you are breaking a habit, not building one
Stopping an existing habit works differently. It usually means changing the cue or the environment rather than counting days. Our guide on how to break a bad habit covers that.
If you want the full research picture
For study designs, limits and what the evidence does not show, read what research says about how habits form.
For how these findings line up with the book's advice on repetition and never missing twice, see our Atomic Habits summary.
Where to go next
Start with one small habit and track it without a deadline. The 30-day habit building plan gives you one step a day for the first month, and you can build a plan around your own cue. More guides live in the habit building hub.
Counting the days helps you see the curve. Track a streak in the day counter, or tick a full run of days in the 100 day challenge tracker.
Because the timing varies so much, record your days instead of counting down to a deadline. The free habit tracker shows your streak and your total days, so one missed day does not erase the month.
